High strength, light weight composite leaf spring and method of making

ABSTRACT

A composite leaf spring comprising a thermoplastic matrix material reinforced with fibers embedded and aligned in the matrix of the composite leaf spring.

CROSS REFERENCE TO RELATED APPLICATION

This patent application claims priority benefit under 35 U.S.C. §119(e)of commonly owned U.S. Provisional Patent Application Ser. No.61/788,800, filed on Mar. 15, 2013, entitled “High Strength, LightWeight Composite Leaf Spring and Method of Making”, the content of whichis incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure is generally directed to leaf springs andparticularly directed to composite leaf springs and methods of makingthe leaf springs for applications, such as automotive and trucksuspension systems.

BACKGROUND

Vehicle manufacturers have long sought to reduce weight of vehicles forthe purposes of improving fuel economy, increasing payload capacity, andenhancing the ride and handling characteristics of automobiles, trucks,utility vehicles, and recreational vehicles. A large proportion ofvehicles employ steel leaf springs as load carrying and energy storagedevices in their suspension systems. While an advantage of steel leafsprings is that they can be used as attaching linkages and/or structuralmembers in addition to their capacity as an energy storage device, theyare substantially less efficient than other types of springs in terms ofenergy storage capacity per unit of mass. Steel leaf springs are heavyby nature, noisy, and subject to corrosion. This weight requiresadditional consideration with respect to mounting requirements, as wellas damping requirements. For instance, shock absorbers are oftennecessary with the use of steel leaf springs in order to control themass of the leaf spring under operating conditions.

Accordingly, what is needed is an alternative leaf spring that canprovide a higher energy per unit mass and thus a lighter weight assemblyconstruction.

SUMMARY

According to aspects illustrated herein, there is provided a compositeleaf spring comprising a thermoplastic matrix material reinforced withfibers embedded and aligned in the matrix of the composite leaf spring.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a hybrid composite leaf springassembly, with a flat second stage, according to embodiments;

FIG. 2 is a cross-sectional view of the primary stage of the hybridcomposite leaf spring of FIG. 1;

FIG. 3 is a schematic illustration of an alternate configuration of acomposite leaf spring assembly comprising a steel main leaf and a flatcomposite second stage load leaf, according to embodiments;

FIG. 3A is a schematic illustration of a further configuration of acomposite leaf spring comprising a steel main leaf and a compositesecond stage load leaf of a curved form, according to embodiments;

FIG. 4 is a schematic illustration of a perspective view of a fullcomposite leaf spring including integrated attachment eyes, according toembodiments;

FIG. 5 is a schematic illustration of a partial perspective view of acomposite suspension control arm, according to embodiments, functioningas a suspension control arm and spring and depicted in a rising ratemounting configuration, according to embodiments;

FIG. 5A is a schematic illustration of a transversely mounted fullcomposite leaf spring, according to embodiments;

FIG. 6 is a partial perspective view of a rear suspension cantilever inframe assembly using another configuration of a composite leaf spring,according to embodiments, comprising a laminate as the locating memberfor the rear axle;

FIG. 7 is a perspective view of a rear suspension cantilever in frameassembly using a further configuration of a composite leaf spring,according to embodiments, comprising a laminate as the locating memberfor the rear axle;

FIG. 8 is a side view of a rear suspension cantilever in frame assemblyusing a further configuration of a composite spring, according toembodiments, comprising a laminate as the locating member for the rearaxle;

FIG. 9 illustrates at FIGS. 9A-9E side views of five types of leafsprings; specifically FIG. 9A illustrates a standard leaf spring; FIG.9B illustrates an eye mounted spring, according to embodiments; FIG. 9Cillustrates a taper ended slide spring, according to embodiments; FIG.9D illustrates a progressive spring, according to embodiments; and FIG.9E illustrates a trailer spring, according to embodiments;

FIG. 10 is a schematic illustration of a composite leaf spring,according to embodiments, comprising stacked, successive layers forminga tapered profile;

FIG. 11 is a schematic illustration of a composite leaf spring,according to embodiments, showing a tapered spring profile obtainedafter successive layers, such as the layers of FIG. 10, are heated andconsolidated;

FIG. 12 is a schematic illustration of a composite leaf spring,according to embodiments, comprising wrapped, successive layers;

FIG. 13 is a schematic illustration of a composite leaf spring,according to embodiments, comprising wrapped, successive layers,attachment eyes and an insert;

FIG. 14 is a schematic illustration of a composite leaf spring,according to embodiments, comprising successive layers, attachment eyesand an insert, and depicted in a curved profile obtained after thelayers are heated and consolidated;

FIG. 15 is a schematic illustration of a composite leaf spring,according to embodiments, showing a tapered spring profile obtainedafter wrapped layers are heated and consolidated;

FIG. 16 is a schematic illustration of a perspective view of amulti-leaf spring, according to embodiments, comprising a flat, fiberreinforced composite second stage. It is noted that three plates aredepicted therein as part of the primary leaf construction, however, moreor less plates could be employed as needed;

FIG. 17 is a schematic illustration of a perspective view of amulti-leaf spring, according to embodiments, comprising a curved, fiberreinforced composite second stage. It is noted that three plates aredepicted therein as part of the primary leaf construction, however, moreor less plates could be employed as needed;

FIG. 18 is a schematic illustration of a perspective view of a compositeleaf spring, according to embodiments, comprising a hybrid leaf, a metalmain leaf, and fiber reinforced thermoplastic composite cladding;

FIG. 19 illustrates schematically at FIGS. 19A and 19B a composite leafspring, according to embodiments, comprising the fiber reinforcedpolymeric (FRP) thermoplastic materials disclosed herein andparticularly shown in a cantilever configuration, actuating against acurved form;

FIG. 20 illustrates schematically at FIGS. 20A and 20B a floatingcantilever construction, according to embodiments;

FIG. 21 is a schematic illustration of a multi-link composite leafassembly, according to embodiments;

FIG. 22 is a schematic illustration another multi-link composite leafassembly, according to embodiments;

FIG. 23 is a schematic illustration of a further multi-link compositeleaf assembly, according to embodiments;

FIG. 24 is a schematic illustration of a full transverse leaf, accordingto embodiments;

FIG. 25 depicts schematically at FIGS. 25A and 25B, a composite leafassembly construction, according to embodiments, with an upper armthereof functioning as a cantilever spring;

FIG. 26 schematically shows a passenger rear suspension sub-assemblyconstruction utilizing coil springs that can be replaced by using afiber reinforced polymeric (FRP) thermoplastic composite leafspring/assembly, as in FIG. 27, according to embodiments;

FIG. 27 schematically shows a rear suspension sub-assembly constructioncomprising the fiber reinforced polymeric (FRP) thermoplastic compositeleaf spring/assembly, according to embodiments;

FIG. 28 schematically shows a further embodiment of the fiber reinforcedpolymeric (FRP) thermoplastic composite leaf spring in curved form;

FIG. 29 depicts a graph showing creep strain versus time for testing ofembodiments of the invention;

FIG. 30 depicts a graph of tensile strength (Psi) for testing ofembodiments of the invention;

FIG. 31 depicts a graph of Youngs Modulus for testing of embodiments ofthe invention;

FIG. 32 depicts a further graph of tensile strength (Psi) for testing ofembodiments of the invention;

FIG. 33 depicts a further graph of Young Modulus for testing ofembodiments of the invention;

FIG. 34 is a graph depicting compression strength for testing ofembodiments of the invention;

FIG. 35 is a graph depicting compression modulus for testing ofembodiments of the invention;

FIG. 36 is further graph depicting compression strength for testing ofembodiments of the invention;

FIG. 37 is a further graph depicting compression modulus for testing ofembodiments of the invention;

FIG. 38 is graph depicting in-plane shear strength for testing ofembodiments of the invention;

FIG. 39 is a graph depicting in-plane shear modulus for testing ofembodiments of the invention;

FIG. 40 is a graph depicting interlaminar shear strength for testing ofembodiments of the invention;

FIG. 41 is a graph depicting creep strain versus time for a specimen 1,according to embodiments of the invention;

FIG. 42 is a graph depicting creep strain versus time for a specimen 2,according to embodiments of the invention and;

FIG. 43 is a graph of stress versus strain for testing of embodiments ofthe invention.

DETAILED DESCRIPTION

The inventors have determined the composite leaf springs disclosedherein comprised of fiber reinforced polymeric (FRP) materials,particularly fiber reinforced thermoplastic materials, can provide muchhigher energy storage per unit mass and therefore a much lighterassembly than, e.g., traditional steel leaf springs. In addition, thefiber reinforced composite leaf springs and assemblies disclosed hereintransmit less noise than steel leaf springs, and require less dampingforce to maintain control under operating conditions.

Thus, the polymer matrix from which the polymeric composite and/orcomposite layers thereof are manufactured comprises a thermoplasticmatrix material, according to embodiments.

Particles or fibers that are embedded in the polymer matrix material toform the thermoplastic composite material can include, but are notlimited to, carbon, glass, Kevlar® fiber, aramid fibers, combinations ofthe foregoing, and the like that are embedded in the polymer matrixmaterial to form the polymer composite material. In addition to theabove-described particles and fibers, iron particles can also beincorporated into the composite material disclosed herein. In thismanner the above-described plies that form the layers of can beinductively heated thereby causing the plies of material to bond and/orcure together.

According to embodiments, fiber reinforced thermoplastic composite leafsprings may generally be comprised of a combination of thermoplasticmatrix materials, high strength reinforcing fibers and other reinforcingmaterials. The thermoplastic matrix material may comprise any materialor combination of materials of a thermoplastic nature suitable for theapplication including, but not limited to: polyvinylidene fluoride(PVDF) which can desirable impart fire resistance properties to theresultant composite materials, polyamide (nylon), polyethylene,polypropylene, polyethylene terephthalate, polyphenylene sulfide,polyetheretherketone, and other thermoplastic polymers and combinationsthereof. The polymeric matrix material may preferably utilize highermolecular weight polyethylene such as ultra-high-molecular-weightpolyethylene (UHMWPE) and high-density cross-linked polyethylene(HDXLPE) and in certain lower performance applications otherpolyethylenes may be used such as cross-linked polyethylene (PEX orXLPE), medium-density polyethylene (MDPE), linear low-densitypolyethylene (LLDPE), and very-low-density polyethylene (VLDPE).

Thermoplastic loading by weight can vary widely depending on physicalproperty requirements of the intended use of the product sheet. Acomposite material may contain about 50 to about 15 wt % thermoplasticmatrix, more preferably about 40 to about 20 wt % and most preferably,about 30 to about 25 wt % of thermoplastic matrix material, by weight ofthermoplastic matrix material plus fibers.

The reinforcing fibers used may include, but are not limited to, glassfibers (such as E-glass and S-glass), aramid fibers (KEVLAR®), carbonfibers, and other high strength fibers and combinations thereof. Otherfibers may also be incorporated, preferably in combination with E-glassand/or S-glass, but optionally instead of E- and/or S-glass. Such otherfibers include ECR, A and C glass, as well as other glass fibers; fibersformed from quartz, magnesia alumuninosilicate, non-alkalinealuminoborosilicate, soda borosilicate, soda silicate, sodalime-aluminosilicate, lead silicate, non-alkaline lead boroalumina,non-alkaline barium boroalumina, non-alkaline zinc boroalumina,non-alkaline iron aluminosilicate, cadmium borate, alumina fibers,asbestos, boron, silicone carbide, graphite and carbon such as thosederived from the carbonization of polyethylene, polyvinylalcohol, saran,aramid, polyamide, polybenzimidazole, polyoxadiazole, polyphenylene,PPR, petroleum and coal pitches (isotropic), mesophase pitch, celluloseand polyacrylonitrile, ceramic fibers, metal fibers as for examplesteel, aluminum metal alloys, and the like.

Where high performance is required and cost justified, high strengthorganic polymer fibers formed from an aramid exemplified by Kevlar maybe used. Other preferred high performance, unidirectional fiber bundlesgenerally have a tensile strength greater than 7 grams per denier. Thesebundled high-performance fibers may be more preferably any one of, or acombination of, aramid, extended chain ultra-high molecular weightpolyethylene (UHMWPE), poly [p-phenylene-2,6-benzobisoxazole] (PBO), andpoly[diimidazo pyridinylene (dihydroxy) phenylene].

In addition, materials such as metals, e.g., aluminum, steel, and otherferrous and/or non ferrous metals, plastics, epoxies, composites, and/orother suitable materials may be used as reinforcements, additives orinserts to impart specific mechanical, dimensional or other physicalproperties either uniformly throughout the spring, or in specificregions of the spring.

It is noted that a particularly suitable combination of materials for acomposite leaf spring according to embodiments is a Nylon matrixreinforced with E-glass fibers.

Various constructions and configurations of leaf springs and assemblies,according to embodiments, are set forth below. It is noted thatadvantageously with respect to the following descriptions andembodiments, any or all of the components of the leaf spring and/orassemblies can be made of the afore-described fiber reinforced polymeric(FRP) composite materials and optional additional reinforcements, and inany combination of materials thereof.

With reference to FIG. 1, a hybrid leaf spring in accordance with afirst embodiment of the present invention is generally designated by thereference number 10. The hybrid leaf spring 10 includes an elongatedprimary leaf 12 having a first modulus of elasticity, a tension surface14, an opposing compression surface 16, and mounting sections 18, shownas, but not limited to, mounting eyes formed integrally with the ends ofthe elongated primary leaf 12 for coupling the primary leaf 12 to avehicle frame. The elongated primary leaf 12 is formed from a suitablematerial, such as but not limited to metal, e.g., steel. Alternatively,the primary leaf 12 may be fabricated from a metal-matrix-compositematerial which can include a plurality of fibers imbedded in a metallicmatrix. Still further, the primary leaf 12 may be made of theafore-described fiber reinforced polymeric (FRP) composite materials andoptional additional reinforcements, and in any combination of materialsthereof.

At least one layer of composite material generally, but not limited to,having an elastic modulus lower than the material of the primary leaf12, is disposed substantially parallel to and bonded to the tensionsurface 14 and the compression surface 16 of the primary leaf 12. Atleast one layer of composite material is preferably formed from aplurality of substantially parallel fibers embedded in a polymericmatrix. As shown in FIG. 1, a first layer of composite material 20 isbonded to the tension surface 14 of the primary leaf 12, and a secondlayer of composite material 22 is bonded to the compression surface 16of the primary leaf 12.

The hybrid leaf spring 10 is typically fabricated by bonding the firstlayer of composite material 20 and the second layer of compositematerial 22 to the primary leaf 12 and placing the assembled componentsin a press employing a heated die having a shape conforming to thedesired unloaded shape of the finished hybrid leaf spring. Thecomponents are then pressed together and through the combination of heatand pressure hybrid leaf springs of consistent repeatable shape can beformed. However, the present invention is not limited in this regard asother fabrication techniques known to those skilled in the pertinentart, such as molding, may be employed.

A clamping means 24 is employed to couple the leaf spring 10 in athree-point configuration to an axle 26 of a vehicle, according toembodiments. In the illustrated embodiment, the clamping means 24includes a pair of U-bolts 28 extending around the axle 26 with the leafspring 10 being received between the U-bolts. A locking plate 30defining two pairs of apertures 32 for receiving ends 34 of the U-bolts28 is positioned adjacent to the second layer of composite material 22and fasteners 36 are threadably engaged with the ends of the U-bolts forreleasably clamping the U-bolts and the leaf spring 10 onto the axle 26.In addition, a load leaf 38 for enhancing the load carrying capacity ofthe leaf spring 10 in the area of highest stress is interposed betweenthe second layer of composite material 22 and the locking plate 30. Theload leaf 38 can be bonded to the second layer of composite material 22or it can be retained in contact with the second layer of compositematerial by the clamping means 24. The load leaf 38 can be either curvedor flat, and may or may not vary in cross-section and be constructed of,e.g., a metallic and/or a composite material.

In order to properly position the leaf spring 10 along the axle 26, apositioner 40 is engaged with the axle 26, according to embodiments, andin the illustrated embodiment of FIG. 1 extends through the leaf spring10, the load leaf 38, and the locking plate 30 and into the axle 26thereby fixing the position of the leaf spring 10 relative to the axle26. The positioner 40 may take various forms, and in the illustratedembodiment is a pin; however, a bolt and so forth can also be usedwithout departing from the scope of the present invention.

Advantageously, the inventors have herein determined that one or all ofthe components of the leaf spring 10 of FIG. 1 can be made of theafore-described fiber reinforced polymeric (FRP) material.

As shown in FIG. 2, to increase bond strength, adhesive layers 42 areinterposed between the primary leaf 12 and each of the first and secondcomposite layers 20, 22 each including a reinforcing layer of sheetmaterial 44, schematically indicated by dashed lines, disposed withinthe adhesive layer 42. Each adhesive layer 42 is preferably a thermosetepoxy adhesive, but may be other types of adhesive without departingfrom the scope of the present invention. For example, the adhesive maybe traditional one or two part liquid structural adhesives such asepoxies, or may be urethanes and thermoplastics.

Another embodiment is shown in FIG. 3 in which previously describedelements bear the same reference numerals. In this embodiment, theprimary leaf is, e.g., a conventional steel primary leaf withoutcomposite layers and the second stage load leaf 138 is a flat fiberreinforced polymeric (FRP) composite structure, according toembodiments, and provides for enhancing the load carrying capacity ofthe leaf spring 10 in the area of highest stress. FIG. 3A shows asimilar leaf spring assembly where the second stage leaf 140 is a curvedFRP composite structure of the invention, providing enhanced secondarysupport of the primary leaf spring with reduced weight and customizedsecondary spring characteristics which are desirable in certain heavyduty applications.

FIG. 4 shows an embodiment of the invention comprising a leaf spring 112made of the afore-described fiber reinforced polymeric (FRP)thermoplastic composite material of the invention with circular eyes 118at each end for attachment to a vehicle chassis. The eyes 118 may, e.g.,be steel or other metal inserts molded and anchored in the compositebody 116 or they may be specially designed composite structures withwound continuous high strength fibers forming the eye in the compositestructure, such as comprising the FRP thermoplastic composite materialsdisclosed herein. The spring also has a mounting area 114, usually at ornear the midpoint between the circular eyes 118, designed to attach toan axle of the vehicle via a clamping mechanism, and with or without useof a sleeve.

As an alternative to the depicted circular eyes 118 of FIG. 4, a linkagecould be employed to secure the structure. Still further, one eye 118could be employed on an end of the leaf 112 with the other end of leaf112 comprising a flat construction instead of a second eye 118.

By way of illustration only, leaf spring 112 could be usable inreplacement of a primary leaf spring 12 in the configuration as shown inFIG. 1, thus potentially providing weight savings and customizablespring characteristics by modification of the types of reinforcement andlayer configuration chosen for a given application. It could also serveas a single stage leaf spring alone where no second stage supplementalsupport is necessary in the application. Such applications may includelight trailer application and so forth.

Accordingly, composite leaf springs in accordance with embodimentsherein, may utilize a single leaf design, as shown in, e.g., FIG. 4, ora multiple stage leaf designs such as, e.g., the leaf spring assemblies,as shown in FIG. 1, FIG. 3 and FIG. 3A.

According to embodiments, other components may be used as structuraland/or locating members of the suspension, and the leaf spring can beused only as, e.g., an energy storage device, in which case the leafspring may or may not employ mounting eyes at the end(s) of the spring.

In some configurations, such as shown in FIG. 5 and FIG. 5A, embodimentsof the invention may be employ a composite control arm 500, which isshown in FIG. 5 in a rising rate mounting configuration. The compositestructure has a mounting hole 502 in the control arm for attachment tothe unsprung portion of the suspension. As shown in FIG. 5A, it may bemounted transversely in the vehicle (not shown), such that thelongitudinal axis of the leaf spring is mounted perpendicular to thefore-aft centerline of the vehicle. The composite structure may have amounting hole 502 in the control arm for attachment to the unsprung(e.g., unloaded, without vehicle weight) portion of the suspension. Thecenter of the leaf spring 504 is attached to the chassis 510, and eachend acts independently, effectively as a cantilever spring, for example,upon the suspension of the vehicle, usually connected directly or via alinkage to the structural members controlling the action of anindividual wheel and tire assembly 512 on the vehicle. In thisembodiment the spring may also function as a structural or locatingmember of the suspension in addition to being an energy storage device.Embodiments may alternatively utilize a circular eye (not shown) whichcould be integrally molded into the composite structure at one or bothends of the leaf spring as an interface with the suspension. Theembodiment shown in FIG. 5 has a mounting hole 502 for the end mountedto the unsprung portion of the suspension. It is noted that any or allof the components depicted in the embodiments of FIG. 5 and FIG. 5A canadvantageously comprise the afore-described fiber reinforced polymeric(FRP) composite material and reinforcements, for obtaining a highstrength, light weight structure and/or assembly.

In additional configurations, shown in FIGS. 6, 7 and 8, a compositeleaf spring 600, according to embodiments, may be used in a rearsuspension cantilever-in frame-assembly, where one end 601 of theassembly is constrained in the chassis 610, 710, 810 and the other end602, 702, 802 acts upon the suspension in an energy storage capacity.The composite leaf spring 600 of FIG. 6 is shown as a multi-stage leafspring. Composite leaf springs 700 and 800 of FIGS. 7 and 8,respectively, are shown as a single stage leaf spring for even lighterweight applications. It is further noted that embodiments may also usethe composite leaf springs disclosed herein as locating or structuraldevices, and may not necessarily employ a circular eye at either end ofthe leaf spring as shown in FIGS. 6, 7 and 8 where the end is fixed tothe axle 612, 712, 812.

FIG. 9 shows front prospective views of five types/configurations ofleaf springs which can comprise the afore-described fiber reinforcedpolymeric (FRP) composite leaf spring components/compositions andoptional additional reinforcements of embodiments of the inventiondisclosed herein, and in any combination, for any or all of the leafspring components.

By way of illustration, a standard spring 902 is initially shown in FIG.9A, wherein, according to embodiments, any or all of the components ofFIG. 9A could advantageously comprise the FRP thermoplastic compositecomposition and optional reinforcements disclosed herein.

FIG. 9B depicts an eye mounted spring 904, according to embodiments,having a center mounting which is flexible, wherein any or all of itscomponents comprise fiber reinforced thermoplastic composite elements.

FIG. 9C depicts a taper ended slide spring 906, according toembodiments, without eye attachments, and similarly having fiberreinforced thermoplastic composite elements for any one or all of itscomponents.

The progressive spring 908 of FIG. 9D, according to embodiments, issimilar to the springs described above with respect to FIGS. 1, 3 and3A, and also comprises fiber reinforced thermoplastic composite elementsfor any or all of its components.

A heavy duty trailer spring 910 is shown in FIG. 9E, according toembodiments, which similarly can have any or all of its leaf componentsas fiber reinforced thermoplastic composite structural elements, asdescribed herein.

Referring now to FIGS. 10-18, depicted therein are variousconfigurations of composite leaf springs, according to embodiments. Asin the case of the embodiments previously described herein, some or allof the components of each of FIGS. 10-18 advantageously comprise theafore-described fiber reinforced polymeric (FRP) thermoplastic compositematerials with optional reinforcements. For example, FIG. 10 is aschematic illustration of a composite leaf spring 200, according toembodiments, comprising stacked, successive layers 210 forming a taperedprofile. It is noted that while the embodiment of FIG. 10 is depictedwithout, e.g., circular eyes, such features could be included therein.This is also the case for other embodiments disclosed herein without thecircular eye features particularly depicted. Moreover, it is furthernoted that the layering or stacking of the various embodiments disclosedherein could also be replaced with a composite plate comprising the FRPthermoplastic materials disclosed herein, and coupled with mechanicalfasteners to, e.g., secure a primary stage leaf to a second stage leaf,and so forth.

FIG. 11 is a schematic illustration of a composite leaf spring 220,according to embodiments, showing a tapered spring profile obtainedafter successive layers, such as the layers 210 of FIG. 10, are heatedand consolidated.

FIG. 12 is a schematic illustration of a composite leaf spring 230,according to embodiments, comprising wrapped, successive layers 240. Itis noted that this embodiment can be employed as a preform comprisingthe afore-described FRP thermoplastic material, which is then heated andconsolidated into the desired final form.

FIG. 13 is a schematic illustration of a composite leaf spring 250,according to embodiments, comprising wrapped, successive layers 240,attachment eyes 118 and an insert 260. As in the case of the othervarious embodiments disclosed herein, all or some of the components ofthe depicted composite leaf spring can comprise the afore-described FRPthermoplastic material. According to embodiments, the curved insert 260depicted therein could also be in other desired shapes, such as flat andso forth, and also be made of a metal, such as steel. The structure ofFIG. 13 can also be employed as a preform, which is then heated andconsolidated achieve, e.g., the structure 270 depicted in FIG. 14.

FIG. 14 is a schematic illustration of a composite leaf spring 270,according to embodiments, comprising heated and consolidated successivelayers, attachment eyes 118 and an insert 260, and depicted in a curvedprofile obtained after the layers are heated and consolidated. It isnoted that to, e.g., reduce the use of material for the structure, thedepicted insert 260 could alternatively be an open spacer, according toembodiments.

FIG. 15 is a schematic illustration of a composite leaf spring 280,according to embodiments, showing a tapered spring profile obtainedafter wrapped layers are heated and consolidated. It is noted that thisembodiment, as well as the other embodiments disclosed herein, could beemployed as both a second and a third stage of a multi-stage leafconstruction.

FIG. 16 is a schematic illustration of a perspective view of amulti-leaf spring 290, according to embodiments, comprising a flat,fiber reinforced composite second stage 300. It is noted that threeplates 310 are depicted therein as part of the primary leafconstruction, however, more or less plates could be employed as needed.

FIG. 17 is a schematic illustration of a perspective view of amulti-leaf spring 320, according to embodiments, comprising a curved,fiber reinforced composite second stage. It is noted that three plates310 are depicted therein as part of the primary leaf construction,however, more or less plates could be employed as needed.

FIG. 18 is a schematic illustration of a perspective view of a compositeleaf spring 330, according to embodiments, comprising a hybrid leafincluding, e.g., a metal main leaf 340 with fiber reinforcedthermoplastic composite material disclosed herein as cladding 350.

The inventors have further determined how to efficiently employ thefiber reinforced polymeric (FRP) thermoplastic material disclosed hereinin various configurations to control the shape (e.g, curvature) of thestructure under loading. For example, a radial form may be utilizedthereby providing a progressive rate increase. Opposing couples at bothends of the structure could be employed, with additional linkages, toprovide desired bending. Moreover, the structure could be made with aconstant stress profile using, e.g., additional machining. By way offurther illustration, FIGS. 19A and 19B depicts a composite leaf spring360, according to embodiments, comprising the fiber reinforced polymeric(FRP) thermoplastic materials disclosed herein and particularly shown ina cantilever, curved form. It is noted that the curved form can controlstress levels and provide rate progression.

FIG. 20 depicts at FIGS. 20A and 20B a floating cantilever construction370, according to embodiments, wherein the cantilever is loaded by acouple applied to one end. Additional linkage may be used to apply anopposing couple to a shackled end, inducing pure bend loading.

FIG. 21 depicts a multi-link composite leaf assembly 380 wherein thelinkage is used to control the geometry. In this embodiment, thecantilever spring 385 is actuated directly by the linkage.

Similarly, FIG. 22 depicts another multi-link composite leaf assembly390 wherein the linkage is used to control the geometry. In particular,the cantilever spring 385 is actuated via the shackle assembly therebyallowing tuning rate progression.

FIG. 23 depicts a further multi-link composite leaf assembly 400 alsoemploying linkage to control the geometry. In this embodiment, thecantilever spring 385 is in a stationary, curved form actuated by thelinkage.

FIG. 24 depicts a fiber reinforced polymeric (FRP) thermoplasticcomposite leaf 410, according to embodiments, in a full transverse leafand shackled configuration.

FIG. 25 depicts at FIGS. 25A and 25B a composite leaf assembly 420,according to embodiments, wherein the upper arm 430 thereof functions asa cantilever spring.

In FIG. 26, a passenger rear suspension sub-assembly construction 440 isshown comprising the fiber reinforced polymeric (FRP) thermoplasticcomposite leaf spring/assembly, according to embodiments, and in FIG. 27a rear suspension sub-assembly construction 450 is shown also comprisingthe fiber reinforced polymeric (FRP) thermoplastic composite leafspring/assembly, according to embodiments, and can function as a directreplacement for an existing chassis. In the depicted embodiment of FIG.27, the left side is shown as direct acting and the right side is shownin a shackled configuration.

A further embodiment of the fiber reinforced polymeric (FRP)thermoplastic composite leaf spring 460 is shown in FIG. 28 in curvedform with circular eyes 118 at each end and comprising a metal, e.g.,steel main leaf 470 with a stress contoured FRP secondary leaf 480. Sucha configuration can provide a reduced weight construction for, e.g.,light truck chassis and can be directly bolted thereto.

A further alternative to bolting for, e.g., light truck applications,can comprise welding and fabrication the composite leaf/assembly,according to embodiments, directly on the frame to accommodatesuspension design.

With regard to the methods of manufacturing, it is noted that thecomposite leaf springs, assemblies and so forth, according toembodiments, can be manufactured by combining the afore-described fiberreinforced polymeric (FRP) thermoplastic material including thereinforcing fibers and other appropriate materials in the presence ofheat and/or pressure, usually in a mold or other device that imparts afinal shape to the completed assembly. The heating and consolidating cantypically be performed at, e.g., between about 400° F. and about 600°F., including between about 450° F. and about 550° F., and at a pressureof, e.g., between about 25 psi and about 100 psi, including about 50psi. It is noted that the pressures employed in manufacturing theconstructions, according to embodiments, are significantly less than thepressures that would be required in the manufacture of thermosetpolymeric articles. Such thermosetting materials, such as epoxymaterials, could in contrast require about 300 psi for construction.Thus, as advantage of embodiments disclosed herein is that reducedpressure may be employed in construction thereby resulting in improvedcost and efficiencies of the overall manufacturing process.

Moreover, a further advantage of embodiments disclosed herein is thatduring, e.g., the heating and consolidating process, the fibers of thefiber reinforced polymeric (FRP) thermoplastic composite leafspring/assembly align by hydraulic action during flow of the polymeric,thermoplastic material. Such alignment provides an increased strengthwhen, e.g., the fibers are in tension and thus also provided anincreased compression strength. It is further noted that the fibers canadvantageously maintain this alignment because of the thermoplasticmaterial flow and hydraulic action thereof, which the inventors havedetermined does not occur with other polymeric materials, such asthermosetting materials.

The final strength and stiffness, as well as other desirable properties,depends upon the thermoplastic material(s) used, as well as the type,size, and orientation of the reinforcements and other materials used. Inaddition, the strength and stiffness of the final product is alsodependent upon the overall dimensional shape of the composite leafspring, including length, width, thickness, and cross-sectional areas.

In some embodiments, the shape of the composite leaf spring may bedeveloped by buildup of layers of pre-impregnated (prepreg) reinforcingmaterials. This buildup of layers is usually inserted into a shaped toolor mold, where heat and/or pressure may be applied to consolidate thematerials.

The shape of the leaf spring may also be developed by the wrapping of apre-impregnated reinforcing material around a pre-shaped core or seriesof cores of suitable material, or around a series of removable cores orpins, in order to develop the cross-sectional profile desired inrelation to the width and length of the spring. This embodiment allowsfor the easy inclusion of mounting eyes which are then encased incontinuous wraps of reinforced material, allowing the use ofconventional mounting systems in a vehicle. Such an embodiment is shownin FIG. 4 where the eyes 118 can be incorporated into a composite leafspring. This pre-wound assembly would then be inserted into a tool ormold and subjected to heat and/or pressure, as required.

In addition, the afore-mentioned wrapping process may also beaccompanied by the application of localized heat to the pre-impregnatedmaterial at or near the point of contact where each successive layer ofpre-impregnated material comes in contact with the previous layer ofpre-wound material in a continuous process. This embodiment would allowpre-formed “blanks” of pre-wound material to be stored for futureshaping and/or further consolidation without the risk of the materialbecoming unwrapped.

EXAMPLES

Testing was conducted to demonstrate various mechanical properties ofthe fiber reinforced polymeric (FRP) thermoplastic composite leafspring/assemblies, according to embodiments of the invention. Suchtesting conditions and results are set forth in detail below.

It is noted that a purpose of the testing was to determine the tensilecreep properties of the specimens using a static load method. Thespecimens, according to embodiments, comprised 70 wt. % glass continuousfiber reinforced polypropylene matrix. The test method employed coversthe determination of tensile or compressive creep and creep-rupture ofplastics under specified environmental conditions. While these testmethods outline the use of three-point loading for measurement of creepin flexure, four-point loading (which is used less frequently) can alsobe used with the equipment and principles as outlined in Test Methods D790. For measurements of creep-rupture, tension is the preferred stressmode because for some ductile plastics rupture does not occur in flexureor compression. The creep test performed here was in a laboratory air,room temperature environment, for a total of 24 hours.

FIG. 29 sets for a graph of test data summary (creep strain) versustime, according to embodiments, and Table 1A below sets forth a tablesummary of creep results. Further details of these fatigue testingresults are also described below.

TABLE 1A ASTM D 2990 Creep Stress (psi) 61097 Load (lbs) 2751 InitialTime (sec) 88 Initial Strain 0.013034 24 Hour Strain 0.020454 24 Creep(ε) 0.007420

Accordingly, testing was conducted to evaluate the mechanical propertiesof fiber reinforced thermoplastic composite material. Specimens,according to embodiments, comprised 70 wt. % glass continuous fiberreinforced polypropylene matrix. It is noted that FIGS. 30-34 referencedbelow include data for 60 wt. % glass reinforced polypropylene.

The testing procedures were performed in accordance with the AmericanSociety for Testing and Materials (ASTM) Standard Test Methods. Inparticular, the ASTM Test Methods included ASTM D 3039 TensileProperties of Fiber Resin Composites, ASTM D 695 Standard Test Methodfor Compressive Properties of Rigid Plastics, ASTM D 5739 Standard TestMethod for Shear Properties of Composite Materials by the V-Notched BeamMethod, ASTM D 2344 Standard Test Method for Short-Beam Strength ofPolymer Matrix Composite Materials and Their Laminates, ASTM E 228Aerospace series—Metallic materials—Test methods; Linear ThermalExpansion of Solid Materials with a Vitreous Silica Dilatometer, ASTM D2990 Standard Test Methods for Tensile, Compressive, and Flexural Creepand Creep Rupture of Plastics, and ASTM D 3479 Standard Test Method forTension-Tension Fatigue of Polymer Matric Composite Materials. Ingeneral, testing was conducted to determine, e.g., strength, modulus,Poisson's ratio, coefficient of thermal expansion, creep and fatiguelife of the specimens in the fiber direction, transverse direction, orshear using a testing machine incorporating one fixed and one movablemember.

The test apparatus used to conduct these ASTM Standard Test Methods isdescribed in the ASTM Standard E 4, Practices for Lad Verification ofTesting Machines. All tests were performed in laboratory air. Thespecimens used to conduct these tests were machined to the nominaldimensions described in each specification. Tabs made from the samematerial as the specimens were bonded to the specimens using FM-73adhesive. Load was applied to the specimens by the MTS 100 kNservohydraulic test frame with digital controller and data acquisition.Hydraulic grips incorporating wedges with non-aggressive surfaces (at agrip pressure of up to 2000 Psi) were used. Strain indicators (gages),along with extensometers were used to determine the strain, and the MTSload frame was used to determine the corresponding loads. Theextensometer may be provide strain information up to specimen failure.

These standards could be used to measure and describe the response ofmaterials, products, or assemblies to mechanical and thermal loads undercontrolled laboratory conditions. Results of the testing may be used aselements of a load-capability assessment or a load-survivabilityassessment which takes into account all of the factors which arepertinent to an assessment of the load capability or load survivabilityof a particular end use.

The test matrix for all specimens is shown in Table 1.

TABLE 1 Test Matrix ASTM Qty Test Designation 5 Fiber Direction TensileStrength & Modulus D-3039 5 Transverse Direction Tensile Strength &Modulus D-3039 5 Fiber Direction Compression Strength & Modulus D-695 5Transverse Direction Compression Strength & D-695 Modulus 5 In-PlaneShear Strength & Modulus (IOSEPESCU) D-5379 3 Fiber & TransverseCoefficient of Thermal E-228 Expansion 3 Transverse DirectionCoefficient of Thermal E-228 Expansion 2 Room Temperature Ambient Creep(24 Hr) D-2990 1 Tension-Tension Fatigue D-3479

Table 2 sets forth a summary of the average property results for thetesting, and the ASTM Standard Method for each test.

TABLE 2 Test Performed ASTM Average Property Fiber Direction TensileStrength D-3039 40,572 Psi Fiber Direction Tensile Modulus D-30393,637,626 Psi Transverse Direction Tensile Strength D-3039 551 PsiTransverse Direction Tensile Modulus D-3039 508,371 Psi Poisson's RatioD-3039 0.14 Fiber Direction Compression Strength D-695 32,409 Psi FiberDirection Compression Modulus D-695 3,685,869 Psi Transverse DirectionCompression Strength D-695 6156 Psi Transverse Direction CompressionModulus D-695 135,638 Psi In-Plane Shear Strength (IOSEPESCU) D-53793580 Psi In-Plane Shear Modulus (IOSEPESCU) D-5379 147,463 PsiInterlaminar Shear Strength (short beam shear) D-2344 3743 Psi FiberDirection Coefficient of Thermal Expan. E-228 Ref. 5.4 με/F. TransverseDirection Coefficient of Thermal. E-228 Ref. 35.9 με/F. Expan. RoomTemperature Ambient Creep D-2990 24.3 με Tension-Tension Fatigue D-347911750 cycles

Example 1 ASTM D3039 Tensile Properties of Fiber-Resin Composites

The results of a test for determination of the tensile properties ofresin-matrix composites reinforced by oriented continuous ordiscontinuous high-modulus >20 Gpa (>3×10⁶ Psi) fibers. The test wasconducted in accordance with the ASTM Standard Test Method D 3039. Thetensile strength and elastic modulus of the specimens were determinedusing a testing machine incorporating one fixed and one movable member.This can provide a means of determining the tensile strength using thefollowing equation: S=P/bd where: S=ultimate tensile strength, MPa orpsi, P=maximum load, N or lbf, b=width, mm or in., and d=thickness, mmor in. To calculate the modulus of elasticity, the following equation isused: E=(ΔP/Δl)(l/bd) where: E=modulus of elasticity, MPa or psi,ΔP/Δl=slope of the plot of load as a function of deformation within thelinear portion of the curve, l=gage length of measuring instrument, mmor in., b=width, mm or in., and d=thickness, mm or in.

FIGS. 30 and 31 set forth a summary of the ASTM D 3039 test data summaryresults for fiber direction strength and modulus, respectively.

Table 3 below sets forth further test results of the specimens.

TABLE 3 Specimen Strength (psi) Maximum Strain Modulus (Psi) 1 487080.01359 3634968 2 37053 0.01105 3471866 3 33756 0.00921 3790564 4 464050.01342 3818362 5 36938 0.01092 3472370 Average 40572 0.01164 3637626Standard Deviation 6562 0.00185 166469

FIGS. 32 and 33 set forth transverse direction tensile strength andmodulus results, respectively, using ASTM D 3039 testing standard. Table4 below sets forth test results for further specimens.

TABLE 4 Specimen Strength (psi) Maximum Strain Modulus (Psi) 6 5960.00106 530723 7 362 0.00060 516071 8 963 0.00158 551641 9 523 0.00152478909 10  313 0.00036 464512 Average 551 0.00103 508371 StandardDeviation 257 0.00054 36135

Per ASTM Standard Test Method D 3039, Tensile Properties of Fiber-ResinComposites, the average fiber direction tensile strength and elasticmodulus of the fiber reinforced unidirectional thermoplastic composite,according to embodiments, was determined to be 40,572 Psi and 3,637,626,Psi, respectively, and the average transverse direction tensile strengthand elastic modulus was determined to be 551 Psi and 508,371 Psi,respectively. The Poisson's ration for the composite was determined tobe 0.14, according to embodiments.

Example 2 ASTM D 695 Standard Test Method for Compressive Properties ofRigid Plastics

Set forth below are results of testing for determining the compressionproperties of resin matrix composites reinforced by oriented continuousor discontinuous high modulus fibers.

The compression strength and elastic modulus of the specimens weredetermined using a testing machine incorporating one fixed and onemovable member. This test method covers the determination of themechanical properties of unreinforced and reinforced rigid plastics,including high-modulus composites, when loaded in compression atrelatively low uniform rates of straining or loading. Test specimens ofstand shape were employed. For compressive properties of resin-matrixcomposites reinforced with oriented continuous, discontinuous, orcross-ply reinforcements, test may be made in accordance with ASTM D3410.

FIGS. 34 and 35 set forth fiber direction compression strength andmodulus results, respectively, using ASTM D 695. Table 5 below setsforth further specimen test results.

TABLE 5 Specimen Modulus (Psi) Strength (Psi) 1 and Test 3574469 3955862 and a 3468934 29288 3 and b 3731030 32049 4 and c 3787475 30986 5 andd 3867438 30134 Average 3685869 32409 Standard Deviation 161865 4141

FIGS. 36 and 37 set forth transverse direction compression strength andmodulus results, respectively, using ASTM D 695 testing standard. Table6 below sets forth test results for further specimens.

TABLE 6 Specimen Modulus (Psi) Strength (Psi)  6 and e 110161 6199  7and f 129991 6181  8 and g 113723 6027  9 and h 155372 6322 10 and i168941 6050 Average 135638 6156 Standard Deviation 257786 120

Per ASTM Standard Test Method D 695, the average fiber directioncompressive strength and compression modulus of the fiber reinforcedunidirectional thermoplastic composites, according to embodiments, wasdetermined to be 32,409 Psi and 3,685,869 Psi, respectively, and theaverage transverse direction compression strength and compressionmodulus was determined to be 6,156 Psi and 1356,638, respectively.

Example 3 ASTM D 5379 Test Method for Shear Properties of CompositeMaterials by the V-Notched Beam Method

Set forth below are results of testing for determining shear propertiesof resin matrix composites reinforced by oriented continuous ordiscontinuous high modulus fibers by the V-Notched beam method.

The shear strength and modulus of the specimens were determined using atesting machine incorporating one fixed and one movable member. The testmethod covers the determination of the shear properties of compositesmaterials reinforced by high modulus fibers. The composite materialswere continuous fiber or discontinuous fiber reinforced composites inthe following forms: 1) Laminates composed only of unidirectionalfibrous laminate, with the fiber direction oriented either parallel orperpendicular to the loading axis; 2) Laminates composed only of wovenfabric filamentary laminate with the warp direction oriented eitherparallel or perpendicular to the loading axis; 3) Laminates composedonly of unidirectional fibrous laminate, containing equal numbers ofplies oriented at 0 and 90 in a balanced and symmetric stackingsequence, with the 0 direction oriented either parallel or perpendicularto the loading axis; 4) Short-fiber-reinforced composites with amajority of the fibers being randomly distributed. This shear testconcept was originally developed without reference to fiber directionfor use on isotropic materials such as metals or ceramics.

FIGS. 38 and 39 set forth in plane shear strength and in plane shearmodulus, using ASTM D 5379. Table 7 below sets forth further specimentest results.

TABLE 7 Specimen Strength (Psi) Modulus (Psi) 1 3594 152596 2 3502154784 3 3635 152208 4 3588 138318 5 N/A 139407 Average 3580 147463Standard Deviation 56 7922

Per ASTM Standard Test Method D-5379, the average shear strength andmodulus of the fiber reinforced unidirectional thermoplastic composite,according to embodiments, was determined to be 3580 Psi and 147,463,respectively.

Example 4 ASTM D 2344 Standard Test Method for Short-Beam Strength ofPolymer Matrix Composite and their Laminates

Set forth below are results of testing for determining the apparentinterlaminar shear properties of resin-matrix composites reinforced byoriented continuous or discontinuous high modulus fibers by the ShortBeam Shear Method.

The apparent interlaminar shear strength of the specimens was determinedusing a testing machine incorporating one fixed and one movable member.This test method determined the short-beam strength of high-modulusfiber-reinforced composite materials. The specimen was a short beammachined from a curved or a flat laminate up to 6.00 mm (0.25 in.)thick. The beam was loaded in three-point bending. Application of thistest method was for the continuous- or discontinuous-fiber-reinforcedpolymer matrix composites, for which the elastic properties are balancedand symmetric with respect to the longitudinal axis of the beam. FIG. 40sets forth these interlaminar shear strength test results, and Table 8below sets forth further specimen test results.

TABLE 8 Shear Specimen Width (in) Thickness (in) Pmax (lbs) Strength(psi) 1 0.24065 0.11035 145 4095 2 0.24165 0.11135 132 3679 3 0.241450.11145 130 3623 4 0.24110 0.11075 140 3932 5 0.24135 0.11105 139 3890 60.24280 0.11130 130 3608 7 0.24220 0.11095 138 3852 8 0.24185 0.11160126 3501 9 0.24130 0.11125 137 3828 10  0.24165 0.11140 123 3427 Average0.24160 0.11115 134 3743 Standard 0.00060 0.00038 7 210 Deviation

Per ASTM Standard Test Method D 2344, the average apparent interlaminarshear strength of the fiber reinforced unidirectional thermoplasticcomposite, according to embodiments, was 3743 Psi.

Example 5 ASTM E 228 Aerospace Series-Metallic Materials; Linear ThermalExpansion of Solid Materials with a Vitreous Silica Dilatometer

Set forth below are the results of testing for the determination oflinear thermal expansion of resin-matrix composites reinforced byoriented continuous or discontinuous high-modulus fibers. The test wasconducted in accordance with the Vishay Micro-Measurements Tech NoteTN-513-1 (also referenced with respect to ASTM E 228 Standard No. E 228,as noted above).

The linear thermal expansion of the specimens were determined using anoven with a digital controller and a non-expanding ceramic referencespecimen. Tables 9 and 10 below sets forth resultant longitudinalcoefficient of thermal expansion data and transverse coefficient ofthermal expansion data, respectively.

TABLE 9 Specimen με at 71.0 F. με at 130.0 F. CTE (με/F.) Reference 0−393 0 1 0 −86 5.2 2 0 −67 5.5 3 0 −72 5.4 Average 5.4

TABLE 10 Specimen με at 71.0 F. με at 130.0 F. CTE (με/F.) Reference 0−393 0 1 0 1677 35.1 2 0 1775 36.7 3 0 1723 35.9 Average 35.9

Per the forgoing testing, the average fiber direction and transverselinear coefficient of thermal expansion of the fiber reinforcedunidirectional thermoplastic composite, according to embodiments, wasdetermined to be 5.4 με/F and 35.9 με/F, respectively.

Example 6 ASTM D 2990 Standard Test Methods for Tensile, Compressive,and Flexural Creep and Creep-Rupture of Plastics

Set forth below are the results of testing for determining the tensilecreep properties pursuant to ASTM D 2990 testing.

The tensile creep properties of the specimens were determined using astatic load method, which covers the determination of tensile orcompressive creep and creep-rupture of materials under specifiedenvironmental conditions. While these test methods outline the use ofthree-point loading for measurement of creep in flexure, four-pointloading could also be used with the equipment and principles as outlinedin Test Methods D 790. For measurements of creep-rupture, tension is thepreferred stress mode because for some ductile plastics rupture does notoccur in flexure or compression. The creep test performed here was in alaboratory air, room temperature environment, for a total of 24 hours.

FIGS. 41 and 42 set forth creep strain versus time for specimens 1 and2, respectively. Table 11 below sets forth further test data results forthese specimens.

TABLE 11 ASTM D 2990 Creep Spec- Initial 24 Hour imen Stress Load TimeInitial 24 Hour Creep No. (Psi) (lbs) (sec) Strain Strain (μ∈) 1 320001732.613 78 0.008524 0.008791 0.000267 2 32000 1689.254 77 0.0080380.008256 0.000218

Per ASTM Standard Test Method D 2990, the average room temperaturetensile creep strain for 24 hours of the fiber reinforced unidirectionalthermoplastic composite, according to embodiments, was determined to be24.3με.

Example 7 ASTM D 3479 Standard Test Method for Tension-Tension Fatigueof Polymer Matrix Composite Materials

Set forth below are the results of testing for determining thetension-tension fatigue of polymer matrix composite materials. The testwas conducted in accordance with ASTM D 3479, wherein a testing machineincorporating one fixed and one movable member was employed. This testmethod determines the fatigue behavior of polymer matrix compositematerials subjected to tensile cyclic loading. The composite materialtested were in the form of continuous-fiber or discontinuous-fiberreinforced composites for which the elastic properties are speciallyorthotropic with respect to the test direction. This test method was forunnotched test specimens subjected to constant amplitude uniaxialin-plane loading where the loading is defined in terms of a test controlparameter. This test method employed two procedures where each defines adifferent test control parameter: Procedure 1: A system in which thetest control parameter is the load (stress) and the machine iscontrolled so that the test specimen is subjected to repetitive constantamplitude load cycles. In this procedure, the test control parameter maybe described using either engineering stress or applied load as aconstant amplitude fatigue variable; Procedure 2: A system in which thetest control parameter is the strain in the loading direction and themachine is controlled so that the test specimen is subjected torepetitive constant amplitude strain cycles. In this procedure, the testcontrol parameter may be described using engineering strain in theloading direction as a constant amplitude fatigue variable.

FIG. 43 sets forth a stress strain diagram depicting the results of theafore-referenced testing. Tables 12 and 13 below set forth furthertesting results and parameters.

TABLE 12 Ppeak (lbs) 1758 Pvalley (lbs) 176 Cycles to Failure 11750

TABLE 13 Cycles Modulus (Psi) 0 3977405 505 4037072 1010 4030765 20184024557 3036 4014639 4003 4004418 5010 3968809 6019 3908714 7027 37769018004 N/A 9012 N/A 10019 N/A

In view of the afore-referenced described testing, the fiber reinforcedthermoplastic composite material transfers the load to the strong fibersvery well, according to embodiments, and there was virtually no creep inthe longitudinal direction (less than 30 microstrain) due to a loadingequal to 80% of the failure stress. Also, the strain toward the end ofthe 24 hours was almost constant, so no further creep is expected beyond24 hours of loading. The results show a very repeatable CTE over the 3specimens tested in both the longitudinal and transverse directions. Infatigue, again this materials shows great load transfer to the fibers.There was only a minimal loss of modulus over the entire fatigue cyclesto failure. Failure occurred at almost 12000 cycles. For this fiberreinforced thermoplastic composite material, according to embodiments,the longitudinal and transverse strength and modulus tests performed,along with the creep and fatigue, showed consistently that much of theload transfer to the strong continuous fibers was achieved. Thus, theresults from these tests may be able to predict, using simple models(Tsai-Hill, Tsai-Wu, rule of mixtures, etc.) the strength and modulus ofthis material as a function of fiber volume fraction, assuming that thequality of the laminates are consistent with the tested specimens.

Further Testing/Example

It is further noted that additional successful testing of embodiments ofthe invention have also been conducted. For example, fiber reinforcednylon blanks, according to embodiments, were tested (3 samples thereof)with completion of over 1.5 million cycles at 85% flex strength. Theaverage load loss was 3%, no failures.

Although this invention has been shown and described with respect to thedetailed embodiments thereof, it will be understood by those skilled inthe art that various changes may be made and equivalents may besubstituted for elements thereof without departing from the scope of theinvention, and the embodiments can be employed in any combination witheach other. In addition, modifications may be made to adapt a particularsituation or material to the teachings of the invention withoutdeparting from the essential scope thereof. Therefore, it is intendedthat the invention not be limited to the particular embodimentsdisclosed in the above detailed description, but that the invention willinclude all embodiments falling within the scope of the appended claims.

What is claimed is:
 1. A composite leaf spring comprising athermoplastic matrix material reinforced with fibers embedded andaligned in the matrix of the composite leaf spring strengthened by heatand consolidation, wherein the thermoplastic matrix comprises a fiberreinforced polymeric matrix, and the composite leaf spring has aresultant fiber direction compressive strength of at least 32,000 psi asmeasured by ASTM Standard Test Method D 695, with the fibers in tension,and the composite leaf spring comprises a curved portion.
 2. Thecomposite leaf spring of claim 1, wherein the composite leaf springcomprises: an elongated primary leaf element having a compressionsurface, an opposing tension surface, and at least one attachmentsection configured to attach the primary leaf to a vehicle frame,wherein the elongated primary leaf element comprises the thermoplasticmatrix material reinforced with the fibers embedded and aligned in thematrix.
 3. An assembly comprising the composite leaf spring of claim 2,wherein the vehicle frame is an automotive vehicle frame.
 4. Thecomposite leaf spring of claim 2, wherein the elongated primary leafelement is curved.
 5. The composite leaf spring of claim 4, furthercomprising an insert.
 6. The composite leaf spring of claim 2, whereinthe elongated primary leaf element comprises stacked, successive layersforming a tapered profile.
 7. The composite leaf spring of claim 2,wherein the elongated primary leaf element comprises wrapped, successivelayers.
 8. The composite leaf spring of claim 7, further comprising acurved insert.
 9. The composite leaf spring of claim 1, comprising acurved, elongated primary leaf element comprising a metal and claddingover the primary leaf element comprising the thermoplastic matrixmaterial reinforced with fibers embedded and aligned in the matrix. 10.The composite leaf spring of claim 1, wherein the spring is a cantileverspring.
 11. The composite leaf spring of claim 1, wherein the compositeleaf spring has a creep testing load of at least 2,750 pounds and atleast a stress of 61,000 psi as measured by ASTM D
 2990. 12. Thecomposite leaf spring of claim 1, wherein the composite leaf spring hasa shear strength of at least 3500 psi as measured by ASTM Standard TestMethod D
 5379. 13. The composite leaf spring of claim 1, wherein thecomposite leaf spring has an interlaminar shear strength of at least3700 psi as measured by ASTM Standard Test Method D
 2344. 14. Thecomposite leaf spring of claim 1, wherein the matrix material comprisesa material selected from the group consisting of polyvinylidenefluoride, polyamide (nylon), polyethylene, polypropylene, polyethyleneterephthalate, polyphenylene sulfide, polyetheretherketone, andcombinations thereof.
 15. The composite leaf spring of claim 14, whereinthe fibers comprise a material selected from the group consisting ofglass, aramid, carbon, quartz, magnesia alumuninosilicate, non-alkalinealuminoborosilicate, soda borosilicate, soda silicate, sodalime-aluminosilicate, lead silicate, non-alkaline lead boroalumina,non-alkaline barium boroalumina, non-alkaline zinc boroalumina,non-alkaline iron aluminosilicate, cadmium borate, alumina, boron,silicone carbide, graphite, ceramic, metal and combinations thereof. 16.The composite leaf spring of claim 15 wherein the matrix materialcomprises at least one of polyethylene terephthalate and nylon.
 17. Thecomposite leaf spring of claim 16, wherein the fibers comprise glass.18. The composite leaf spring of claim 17, comprising a nylon matrixreinforced with E-glass fibers.
 19. The composite leaf spring of claim15, wherein the heating and consolidating are performed at a temperatureof at least about 400° F. and at a pressure of at least about 50 psi.